1. Field of the Invention
The present invention relates to devices for stacking bound pamphlets or loose sheets conveyed from a finishing station and, more particularly, to devices for stacking the pamphlets or sheets in an offset fashion which facilitates easy separation of the individual pamphlets or sheets from the stack.
2. Prior Art
Many duplicating machines include apparatus for collecting printed paper sheets into stacked sets and then binding the sets together to make pamphlets and the like. It is desirable to provide a stacking apparatus which collects the bound sets and stacks them in an offset fashion which facilitates the separation of the sets from each other by a user.
Many types of stacking devices are known. For example, U.S. Pat. Nos. 4,017,066 and 3,682,328 disclose stacking devices in which individual sets of sheets are stacked in an offset fashion by the use of a pair of paddle wheels having flexible blades. The paddle wheels are disposed at opposite portions of the tray upon which the sets are fed and are alternately activated to drive the sets against opposing walls. Each patent discloses a stacker which utilizes a stacking tray which is raised or lowered to provide a stacking station which does not change in elevation during the stacking process.
A disadvantage with this type of stacking apparatus is that the paddlewheel structure is complex in construction and requires many movable parts. Such types of apparatus also require over-complicated structure to adjust for sheets of varying sizes. Indeed, some stacks are unable to adjust for sheets of varying sizes at all.
Another example is disclosed in U.S. Pat. No. 4,208,122. This patent is directed to a stacking device which utilizes a fixed tray having a reciprocating pawl which moves to offset the sets of sheets deposited onto the fixed tray by a contiguous duplicating machine. The stacking assembly also includes a claw which is rotatably mounted to the duplicating machine which serves to skew the sets with respect to one another in addition to their being offset. A disadvantage of this type of apparatus is that it lacks sufficient means for guiding the sheets into their offset stacked relation so that the resulting stack may be unbalanced and difficult to convey. In addition, the lack of a moving tray creates additional problems in guiding the sets from the feeding station to their position in the stack.
Another example of a stacking device is disclosed in U.S. Pat. No. 4,033,579. This device includes a movable tray which is indexed within an enclosure having perforations formed in its upper portion which communicate with sources inducing a vacuum. A vacuum is created to position sheets or sets fed onto the tray against two fixed walls disposed normally to each other. The device includes a finger which is rotatably mounted to the enclosure and is lifted up and down against the stack to maintain the stacked sheets in position as additional items are being placed onto the stack.
A disadvantage of this type of system is requirement of a source of vacuum and the use of air flow to position the sheets. This type of system has inherent noise problems created by the rush of air through the orifices formed in the enclosure, and may create problems resulting from the leakage of ambient air into the enclosure, especially if the ambient air is laden with dust or other contaminants which may deposit themselves on the stacked items or clog the orifices. Another disadvantage is that many of the design tolerances must be high to prevent leakage of air from seams between different components.
A different type of stacking apparatus is disclosed in U.S. Pat. No. 3,860,127. This stacking device utilizes a fixed tray which includes a rotating jogger arm which reciprocates in a vertical plane between two coplanar vertical surfaces that provide a fixed wall. Sheets are fed onto the tray and alternately abut either the fixed wall or a flat surface of the jogger arm which is rotated into place to engage alternate sets of sheets as they are fed onto the tray. A disadvantage of this type of apparatus is that the rotating jogger arm must be mounted on a vertically movable carriage that is indexed upward as the stack of sheets increases in height. This adds to the complexity of the structure of the stacker and may present problems in enlarging the overall dimensions of the stacker so that it may not be capable of operation within a standard office environment.
Another type of stacker is disclosed in U.S. Pat. No. 2,918,852. This stacker utilizes a reciprocating tray and a pair of opposed jogger arms which alternately rotate into and out of a sheet engaging position. A disadvantage of this system lies in the number and complexity of the components required for the stacker. The use of two jogger arms requires that space be provided both laterally and in a vertical dimension to accommodate the cylinders and linkage required to activate the jogger arms. In addition, the device requires a pair of opposing fixed walls, each interacting with an opposing jogger arm. This requires additional mounting and positioning structure.
Accordingly, a need exists for an offset stacking assembly which minimizes the amount and complexity of the components required to accomplish the stacking operation, a stacking assembly which possesses minimal height, width, and depth requirements so that it may be positioned within a standard office environment, and a stacking assembly which includes a movable tray so that stacked sheets or bound pamphlets may be removed from the stacker and presented to a user at an optimum elevation above the floor.